//1.
#include<stdio.h>

int main()
{
	int i,n,sum;
	printf("input n:");
	scanf("%d",&n);
	
	for(i = 1; i <= n; i++)
	{
		if(i % 2 == 1)
			sum += i;
	}
	printf("add = %d\n",sum);
	
	return 0;
}
